The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, the present patent application concerns the field of the manufacture of composite material workpieces with stiffeners, in particular for aeronautics.
For reasons of mass and cost gains, it is interesting to replace metal parts with composite parts, in particular structural parts with complex geometry.
Most of the composite workpieces are manufactured from a fibrous reinforcement stack, frequently called “plies,” for example carbon fibers or glass fibers, which are subsequently injected with resin, this resin being generally polymerized by temperature rise.
This technology is generally satisfactory for stressed monolithic workpieces according to their plane, but may prove unsuitable for “out-of-plane” stressed structures.
Thus, it is known to equip some workpieces with a stiffener of T-shaped section for example, which is positioned perpendicularly, or at a certain angle, to the main plane of the workpiece.
The stiffener is generally formed by a first L-shaped member and a second L-shaped composite material member which are arranged back-to-back to form a T.
More particularly, each stiffener includes a base which is extended on the soleplate of the workpiece, and a rib which extends from the associated base to form the web of the stiffener.
The rib and the base of each L-shaped member are connected by a bent connecting portion.
The junction area of the L-shaped members and the soleplate of the workpiece, in the vicinity of the connecting portions of the L-shaped members, generally delimits a cavity which is filled with resin, or else which forms a disturbance of the flatness of the plies which tend to close this cavity.
This junction area may constitute a mechanical weakening which may cause an unfolding of the plies of the connecting portion of the L-shaped members and a delamination of the plies between each member L and the soleplate of the workpiece.
Indeed, the composite workpiece may be subject, among other things, to forces collinear with the direction of the web formed by the ribs of the L-shaped members.
This type of stress may cause unfolding of the bent connecting portions of the L-shaped members, resulting in a premature delamination of the workpiece.
The presence of this first damage at relatively low forces reduces the use of the workpiece in structural areas.
In order to reinforce the workpiece, it is known to make seams to bond the plies to each other, in particular to bond the L-shaped members on the soleplate of the workpiece. This type of process and workpiece is for example described in the documents FR-A-2993492 and EP-A-2540479.
Such seams allow reinforcing the workpiece but are not entirely satisfactory.
Indeed, it is observed that the tension of the thread, especially in the junction area of the bent connecting portions of the L-shaped members and the soleplate of the workpiece, is not sufficient to take over the unfolding stresses.
When the threads are not sufficiently taut, it is necessary to sufficiently deform the workpiece in order to allow the thread to be tensioned and thus play its role of reinforcement.
The deformation necessary for the tensioning of the thread is often sufficient to cause cracking and other delamination detrimental to the holding of the workpiece.